Method and system for diagnosing and/or controlling a reciprocating engine having a variable compression ratio

Abstract

The invention relates to a method for diagnosing and/or controlling a reciprocating engine having a variable compression ratio, wherein the method comprises the working steps: determining (S30) a first value (U.sub.1,1, U.sub.1,2; Δ.sub.1) of a rotational irregularity parameter of a crankshaft (1) of the reciprocating engine; and determining (S60) a value of a compression ratio parameter for the reciprocating engine based on said first rotational irregularity parameter value.

Claims

1. A method of diagnosing or controlling a reciprocating piston engine with a variable compression ratio, comprising: detecting at least one of a crank angle of a crankshaft of the reciprocating piston engine and at least one time derivative of the crank angle; determining a first value of a rotational irregularity parameter of the crankshaft on the basis of the at least one of the detected crank angle and the at least one time derivative for a first target compression ratio of at least a first cylinder of the reciprocating piston engine, wherein the first value of the rotational irregularity parameter is determined for at least one specified crank angle region extending over from at least 2° to at most 135° and comprising at least one of a top dead center and a bottom dead center of the first cylinder; changing a target compression ratio of the first cylinder of the reciprocating piston engine from the first target compression ratio to a second target compression ratio; determining a second value of the rotational irregularity parameter of the crankshaft for the second target compression ratio; determining a value of a compression ratio parameter for the reciprocating piston engine on the basis of the first and second values of the rotational irregularity parameter; and outputting a signal if the value of the compression ratio parameter satisfies a specified condition.

2. The method according to claim 1, wherein changing the target compression ratio further comprises: changing a target length of a piston rod of the first cylinder of the reciprocating piston engine.

3. The method according to claim 1, further comprising: determining at least one of the first value and the second value of the rotational irregularity parameter for an unfired operation of the first cylinder of the reciprocating piston engine.

4. The method according to claim 1, wherein the least one specified crank angle region extends over from at least 10° to at most 45°.

5. The method according to claim 1, further comprising: filtering at least one of the detected crank angle and the at least one time derivative of the crank angle; and determining the first value or the second value of the rotational irregularity parameter on the basis of the filtered crank angle or the at least one filtered time derivative.

6. The method according to claim 1, wherein at least one of the first value and the second value of the rotational irregularity parameter is determined on the basis of at least one average value or at least one extreme value.

7. A system for diagnosing or controlling a reciprocating piston engine with a variable compression ratio, comprising: a sensor for detecting at least one of a crank angle of a crankshaft of the reciprocating piston engine and at least one time derivative of the crank angle; and an engine control unit for: determining a first value of a rotational irregularity parameter of the crankshaft on the basis of the at least one of the detected crank angle and the at least one time derivative for a first target compression ratio of at least a first cylinder of the reciprocating piston engine, wherein the first value of the rotational irregularity parameter is determined for at least one specified crank angle region extending over from at least 2° to at most 135° and comprising at least one of a top dead center and a bottom dead center of the first cylinder; changing a target compression ratio of the first cylinder of the reciprocating piston engine from the first target compression ratio to a second target compression ratio; determining a second value of the rotational irregularity parameter of the crankshaft for the second target compression ratio; determining a value of a compression ratio parameter for the reciprocating piston engine on the basis of the first and second values of the rotational irregularity parameter; and outputting a signal if the value of the compression ratio parameter satisfies a specified condition.

8. The system according to claim 7, wherein the least one specified crank angle region extends over from at least 10° to at most 45°.

9. The system according to claim 7, wherein changing the target compression ratio further comprises: changing a target length of a piston rod of the first cylinder of the reciprocating piston engine.

10. The system according to claim 7, wherein the engine control unit is further operable to: determine at least one of the first value and the second value of the rotational irregularity parameter for an unfired operation of the first cylinder of the reciprocating piston engine.

11. The system according to claim 7, wherein at least one of the first value and the second value of the rotational irregularity parameter is determined on the basis of at least one average value or at least one extreme value.

12. A motorized vehicle, comprising: a reciprocating piston engine with a variable compression ratio that includes a first cylinder coupled to a crankshaft by a piston rod having an adjustable length; and a system for controlling the reciprocating piston engine which includes: a sensor for detecting at least one of a crank angle of the crankshaft and at least one time derivative of the crank angle; and an engine control unit for: determining a first value of a rotational irregularity parameter of the crankshaft on the basis of the at least one of the detected crank angle and the at least one time derivative for a first target compression ratio of at least the first cylinder of the reciprocating piston engine, wherein the first value of the rotational irregularity parameter is determined for at least one specified crank angle region extending over from at least 2° to at most 135° and comprising at least one of a top dead center and a bottom dead center of the first cylinder; changing a target compression ratio of the first cylinder of the reciprocating piston engine from the first target compression ratio to a second target compression ratio; determining a second value of the rotational irregularity parameter of the crankshaft for the second target compression ratio; determining a value of a compression ratio parameter for the reciprocating piston engine on the basis of the first and second values of the rotational irregularity parameter; and outputting a signal if the value of the compression ratio parameter satisfies a specified condition.

13. The motorized vehicle according to claim 12, wherein the least one specified crank angle region extends over from at least 10° to at most 45°.

14. The motorized vehicle according to claim 12, wherein changing the target compression ratio further comprises: changing a target length of the piston rod of the first cylinder of the reciprocating piston engine.

15. The motorized vehicle according to claim 12, wherein the engine control unit is further operable to: determine at least one of the first value and the second value of the rotational irregularity parameter for an unfired operation of the first cylinder of the reciprocating piston engine.

16. The motorized vehicle according to claim 12, wherein at least one of the first value and the second value of the rotational irregularity parameter is determined on the basis of at least one average value or at least one extreme value.

Description

(1) Further advantageous developments of the present invention become clear from the dependent claims and the following description of preferred embodiments. The figures show, partly schematically;

(2) FIG. 1 shows a part of a motorized vehicle according to an embodiment of the present invention;

(3) FIG. 2 shows a rotational irregularity over a crank angle of a crankshaft of the motorized vehicle for a maximum and minimum compression ratio; and

(4) FIG. 3 shows a method of diagnosing a reciprocating piston engine of the motorized vehicle according to an embodiment of the present invention.

(5) FIG. 1 shows a part of a motorized vehicle with a reciprocating piston combustion engine with a variable compression ratio and a system for diagnosing the reciprocating piston engine according to an embodiment of the present invention.

(6) The reciprocating piston engine comprises, in a manner known in principle, a crankshaft 1 and several cylinders 10, 20, 30 and 40, in which pistons compress a fuel/air mixture (see cylinder 10), are driven by combustion of the mixture (see cylinder 20), take in (see cylinder 30) and exhaust (see cylinder 40) air or mixture in turn, and are coupled to the crankshaft 1 by means of piston rods 11, 21, 31 and 41 for this purpose.

(7) The length of the piston rods 11, 21, 31, 41 and therefore the compression ratio of the cylinders 10, 20, 30 and 40 or of the reciprocating piston combustion engine is adjustable by means of an Engine Control Unit (ECU) 2, as indicated by a dash-dotted line in FIG. 1.

(8) The ECU 2 detects a crank angle KW by means of a trigger wheel 3 and determines rotational irregularity parameter values therefrom.

(9) FIG. 2 shows, by way of example, a rotational irregularity Ω determined by the ECU 2 for a maximum compression ratio (solid line in FIG. 2) and a minimal compression ratio (dash-dotted line in FIG. 2). The rotational irregularity Ω can for example be a variation of a crankshaft speed over crank angle

(10) $\frac{\mathrm{dKW}}{\mathrm{dt}}\left(\mathrm{KW}\right),$
a crankshaft acceleration over crank angle

(11) $\frac{d^2\mathrm{KW}}{{\mathrm{dt}}^2}\left(\mathrm{KW}\right)$
or similar.

(12) The graphs illustrate, by way of example, that a rotational irregularity Ω of the crankshaft 1 is dependent on the current compression ratio in a characteristic manner, and in particular that it varies in a characteristic manner with the set compression ratio.

(13) The ECU 2 carries out a method—subsequently explained in relation to FIG. 3—for diagnosing the reciprocating piston engine according to an embodiment of the present invention or is configured in terms of its hardware and software to do so.

(14) The ECU 2 or the method checks in a step S10 whether a diagnosis condition is satisfied, in particular whether the reciprocating piston engine is in an unfired engine breaking mode or not.

(15) In a further development, the diagnosis condition can additionally implement a cyclical operation of the method, in particular once in a specified drive cycle, for example by additionally checking a corresponding (drive) cycle indicator or flag. In a corresponding manner, the subsequent steps are carried out according to an embodiment during each engine brake operation or instead only once per drive cycle.

(16) If the diagnosis condition is not satisfied (S10, “N”), the ECU 2 or the method repeats step S10. Otherwise, the ECU 2 or the method proceeds with step S20.

(17) Here, the ECU 2 or the method specifies (by means of a corresponding target specification for the adjustment of the piston rod lengths) a maximum target compression ratio (of cylinders 10, 20, 30, 40) of the reciprocating piston engine, detects for or at this target compression ratio a time sequence of crank angles KW(t) and determines therefrom, using numerical filtering, the rotational irregularity Ω of the crankshaft 1 (solid line in FIG. 2).

(18) From this, the ECU 2 or the method determines a first value of a rotational irregularity parameter in a step S30.

(19) This can for example be a maximum value U.sub.1,1 of the rotational irregularity Ω in a specified crank angle region δ.sub.1 around a top dead center OT of a first cylinder 10, a minimum value U.sub.1,2 of the rotational irregularity Ω in a specified crank angle region δ.sub.2, which comprises the top dead center OT, a difference Δ.sub.1 between the maximum value and the minimum value in the specified crank angle region δ.sub.2 or such like.

(20) In a step S40 the ECU 2 or the method specifies (by means of a corresponding target specification for the adjustment of the piston rod lengths) a minimum target compression ratio (of cylinders 10, 20, 30, 40) of the reciprocating piston engine and in turn determines, for or at this target compression ratio, the rotational irregularity Ω of the crankshaft 1 (dash-dotted line in FIG. 2) from the detected time sequence of crank angles, using numerical filtering.

(21) From this, the ECU 2 or the method determines, in a step S50, in a manner analogous to step S30, a second value of the same rotational irregularity parameter, that is for example a maximum value U.sub.2,1 of the rotational irregularity Ω in the specified crank angle region δ.sub.1 around a top dead center OT of a first cylinder 10, a minimum value U.sub.2,2 of the rotational irregularity Ω in the specified crank angle region δ.sub.2 or a difference Δ.sub.2 between the maximum value and the minimum value in the specified crank angle region δ.sub.2.

(22) In a step S60, the ECU 2 or the method then determines, on the basis of the first and second rotational irregularity parameter values, for example on the basis of a difference between the two values (U.sub.2,1−U.sub.1,1), (U.sub.2,2−U.sub.1,2) or (Δ.sub.2−Δ.sub.1), a compression ratio parameter value, which is for example proportional to this difference and is dependent on a change of the compression ratio or specifies this.

(23) In a step S70, the ECU 2 or the method checks whether this compression ratio parameter value lies outside a specified region, in particular whether it falls below a specified minimum value which is supposed to be achieved (at least) during the course of a change of the compression ratio between a maximum value and a minimum value.

(24) If this is not the case or if the compression ratio parameter value lies within the specified region (S70; “N”), the ECU 2 or the method returns to step S10 in order to carry out the process again if the diagnosis condition is satisfied, for example in a subsequent drive cycle or during engine break operation.

(25) Otherwise, or in the case of a deviation between the rotational irregularity parameter values for the maximum and minimum target compression ratios or their differences being too small (S70: “Y”), the ECU 2 or the method outputs a corresponding diagnosis signal in a step S80, which diagnosis signal indicates an unsatisfactory function or a malfunction of the adjustment mechanism and then returns to step S10.

(26) Although exemplary embodiments have been discussed in the preceding description, it is noted that a variety of modifications are possible.

(27) In this way, in the embodiment, the target lengths of all piston rods 11, 21, 31 and 41 or the target compression ratios of all cylinders 10, 20, 30 and 40 were adjusted uniformly and deviations of the rotational irregularity Ω of the crankshaft 1 resulting therefrom were taken into account only for the first cylinder 10.

(28) In a modification, the method described above can be carried out for each of the (other) cylinders in an analogous manner, in particular their top dead centers and/or bottom dead centers can also be taken into account, and in step S80 a diagnosis signal, in particular a differentiated or individual diagnosis signal, can be output if for (at least) one of the cylinders 10, 20, 30 and 40 an unsatisfactory function or a malfunction of the corresponding piston rod 11, 21, 31 or 41 is detected, in particular the corresponding cylinder can be specified. For example, if the difference between the maximum value for the minimum and maximum compression ratio lies within the specified region for the specified crank angle region δ.sub.1 of the first cylinder 10, but not for a corresponding further specified crank angle region around the top dead center of a further cylinder 20, then a malfunction of this cylinder 20 is indicated in the step S80 according to the modification.

(29) Insofar as the piston rods or the compression ratios are individually adjustable, it is possible, according to a variant, to change only one target length or one target compression ratio for a cylinder and to diagnose only this cylinder in steps S20, S40, wherein, in a further development of this variant, all cylinders are checked successively, that is the steps S10 to S80 can be carried out individually for all cylinders.

(30) In a variant, for example an average value over the specified crank angle region δ.sub.1 can also be used instead of the maximum value U.sub.1,1 or U.sub.2,1 as rotational irregularity parameter value.

(31) In a variant, the changing of the target length or of the target compression ratio can also be omitted. Accordingly, as in particular illustrated in FIG. 2, the presence of a maximum actual compression ratio or a compression ratio parameter value corresponding thereto can be determined from the characteristic rotational irregularity parameter values U.sub.1,1, U.sub.1,2 or Δ.sub.1 alone, the presence of a minimum actual compression ratio or a compression ratio parameter value corresponding to this can be determined from U.sub.2,1, U.sub.2,2 or Δ.sub.2 alone, and other actual compression ratios or corresponding compression ratio parameter values from intermediate values thereof.

(32) These can additionally or alternatively be used, according to a further variant, for controlling, in particular regulating, the reciprocating piston combustion engine, in particular for the setting of the compression ratio, for example by outputting corresponding control signals in step S80.

(33) Additionally, it is noted that the exemplary embodiments merely concern examples which are not intended to restrict the scope of protection, the applications and the structure in any way. Instead, the skilled person is being given a guideline by means of the preceding description for implementing at least one exemplary embodiment, whereby various modifications, in particular as regards the function and arrangement of the described components, can be carried out within the scope of protection as it results from the claims and combinations of features equivalent thereto.

LIST OF REFERENCE SIGNS

(34) 1 Crankshaft

(35) 2 Engine Control Unit (ECU)

(36) 3 Trigger wheel

(37) 10; 20; 30; 40 Cylinder

(38) 11; 21; 31; 41 Piston rod

(39) KW Crank angle

(40) Ω Filtered rotational irregularity

(41) OT Top dead center

(42) δ.sub.1; δ.sub.2 Specified crank angle region

(43) U.sub.1,1; U.sub.2,1 Maximum value

(44) U.sub.1,2; U.sub.2,2 Minimum value

(45) Δ.sub.1; Δ.sub.2 Difference